论文标题

通过旋转的多维电子散射的旋转机器学习探测原子尺度对称性破坏

Probing atomic-scale symmetry breaking by rotationally invariant machine learning of multidimensional electron scattering

论文作者

Oxley, Mark P., Ziatdinov, Maxim, Dyck, Ondrej, Lupini, Andrew R., Vasudevan, Rama, Kalinin, Sergei V.

论文摘要

4D扫描透射电子显微镜(STEM)方法启用了固体在原子量表上的结构和功能的映射,产生了包含有关原子质电气和磁场,结构和电子订单参数的信息的信息丰富的数据集,以及其他对称性破坏。在利用4D型材料探索的途径上的关键瓶颈是分析工具的缺乏,可以将复杂的4D-STEM数据集减少到物理相关的描述符中。经典的机器学习(ML)方法(例如主组件分析)和其他线性构造技术受到多点组对称变体的限制,其中每个旋转等效位置的衍射图将形成其自己的组件。该限制甚至适用于更复杂的ML方法,例如卷积神经网络。在这里,我们提出并实施了一种使用旋转不变的变异自动编码器(RRVAE)从4D-STEM数据集中对对称性破坏现象进行系统探索的方法,该方法旨在将对象的一般旋转从其他潜在表示中删除。讨论了纯旋转RRVAE的实现,以及用于模拟石墨烯和锌蓝色结构的模拟数据的应用,这些数据说明了现场对称性破坏的影响。最后,说明了石墨烯中空缺的4D茎数据的RRVAE分析,并将其与经典的质量中心(COM)分析进行了比较。这种方法是通用的,用于探测复杂系统中的对称性破坏现象,可以针对探索系统的2D衍射空间的广泛衍射方法实现,包括X射线Ptychography,电子反向散射衍射(EBSD)和更复杂的方法。

The 4D scanning transmission electron microscopy (STEM) method has enabled mapping of the structure and functionality of solids on the atomic scale, yielding information-rich data sets containing information on the interatomic electric and magnetic fields, structural and electronic order parameters, and other symmetry breaking distortions. A critical bottleneck on the pathway toward harnessing 4D-STEM for materials exploration is the dearth of analytical tools that can reduce complex 4D-STEM data sets to physically relevant descriptors. Classical machine learning (ML) methods such as principal component analysis and other linear unmixing techniques are limited by the presence of multiple point-group symmetric variants, where diffractograms from each rotationally equivalent position will form its own component. This limitation even holds for more complex ML methods, such as convolutional neural networks. Here, we propose and implement an approach for the systematic exploration of symmetry breaking phenomena from 4D-STEM data sets using rotationally invariant variational autoencoders (rrVAE), which is designed to disentangle the general rotation of the object from other latent representations. The implementation of purely rotational rrVAE is discussed as are applications to simulated data for graphene and zincblende structures that illustrate the effect of site symmetry breaking. Finally, the rrVAE analysis of 4D-STEM data of vacancies in graphene is illustrated and compared to the classical center-of-mass (COM) analysis. This approach is universal for probing of symmetry breaking phenomena in complex systems and can be implemented for a broad range of diffraction methods exploring the 2D diffraction space of the system, including X-ray ptychography, electron backscatter diffraction (EBSD), and more complex methods.

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